With high torque and sticky tires, axle wind up (actually spring wind up) can still occur even with Super Stock leaf springs installed and a properly adjusted pinion-snubber. In this situation, the forward section of the leaf spring itself actually distorts, bending upward in an S-shape, allowing the axle to rotate. There is still another trick you can perform to help eliminate spring wind up of this type, and it involves installing clamps on the forward section of each leaf spring. By adding either bolted on clamps, or by wrapping red-hot mild steel around the leaves, just behind the leading edge of the lower leaf, distortion will be minimized and axle wrap up reduced significantly.

Pinion Angle

Pinion angle is also an important part of rear suspension setup, and the ideal pinion angle can vary from application to application. The idea here is to have enough positive angle (pinion angled toward ground when compared to the driveshaft), so that when the axle wraps up, the pinion gear and the driveshaft are at a neutral, or zero angle. In four-link cars, the necessary pinion angle can be as little as one or two degrees, in ladder bar cars, four to five degrees is a good starting point. For a leaf-spring application, we’ve seen as much as eight to ten degrees of pinion angle necessary for proper driveshaft alignment under power. The best advice here is trial and error, and for more reading regarding pinion angle and other aspects of rear suspension setup we recommend the book Doorslammers: The Chassis Book by Dave Morgan.

CalTracs

While factory Chrysler leaf spring rear suspensions work very well in both street and performance applications, modern technology has taken leaf spring rear suspensions a step further in recent years. Calvert Racing has upgraded suspension components in the form of their CalTracs traction bars that can be used with factory style multi-leaf rear springs, or with Calvert Racing’s split mono-leaf leaf springs. The function of the CalTracs is essentially the same as the pinion snubber, to eliminate axle wind up, but the CalTracs do a much more efficient job. By using pivot assemblies at the forward spring hanger, and adjustable link bars between the forward hanger and the shock mount under the differential, axle wind up force is transferred to the top of the forward section of the leaf spring, preventing it from distorting.

We have used the CalTracs system both with stock springs and with the Calvert split mono-leaf springs, and found the CalTracs setup to be very effective. Installing CalTracs on our B3 project resulted in harder launches, higher wheel-stands, improved 60-foot times, and reduced elapsed times. To see a full installation of the CalTracs rear suspension on our ’64 Dodge Nostalgia Super Stock project, check out the August 2013 issue of Mopar Muscle. The CalTracs system is simple to install, easy to adjust, and adaptable to applications from mild street cars to 7-second outlaw drag cars.

Other Considerations

A car’s rear shocks, front suspension, and overall chassis stiffness, also greatly affects how the car will perform on the street and the track. 50/50 ratio rear shocks are the best all-around choice for the rear, and adjustable or double-adjustable rear shocks allow adjustments for differing track and road conditions. Most Mopars are nose heavy, and in straight-line applications such as drag racing, a Mopar will benefit from getting the front of the car up in the air, transferring the cars weight to the rear tires. Lighter rate torsion bars will allow easier front end travel, as will eliminating or disconnecting the front sway bar if so equipped.

The best way to enhance weight transfer is by installing 90/10 or adjustable race shocks (adjusted for easy extension and hard compression), in the front suspension. A 90/10 shock allows light force to extend the shock (only 10 percent of total force) and heavy force to compress the shock (90 percent of total force), allowing the front of the car to rise, and then stay there keeping more weight on the rear tires. We’ll get more in depth with front suspensions in a future issue of Mopar Muscle.

Chassis stiffness is another consideration in the overall performance of your car, and items like subframe connectors, torque boxes, and a roll cage can affect your suspension in a positive way. The less a car flexes, the more the suspension can do what it’s supposed to. Subframe connectors are available in bolt-in style, or can be welded in place. For the best stiffening, frame connectors from US Car Tool are form fitted and welded to the car’s floor, creating a complete box frame section. In extreme applications a roll bar, or roll cage, will tie the chassis together offering overall stiffness to the suspension and safety to the driver.

SOURCE
Performance Online
2572 E. Fender Ave. Unit #A
Fullerton
CA  92831
800-638-1703
http://www.performanceonline.com
Calvert Racing
42156 10th Street West, Unit V
Lancaster
CA  93534
661-948-1490
www.calvertracing.com
AR Engineering
Portland
OR
www.arengineering.com
U.S. Car Tool
919-855-8200
uscartool.com/